The present invention relates to a self-supporting tire for vehicle wheels, comprising: a carcass structure having at least one carcass ply provided with end flaps in engagement with respective annular anchoring structures disposed in coaxial relation with a geometric rotation axis of the tire at axially spaced apart positions with respect to each other; a belt structure applied to the carcass structure at a radially outer position thereof; a tread band applied to the belt structure at a radially outer position thereof; at least one pair of sidewalls applied to the carcass structure at opposite side positions; at least one pair of resilient stiffening inserts incorporated into the carcass structure, each at one of said sidewalls.
The present invention also relates to a method of manufacturing a self-supporting tire for vehicle wheels, comprising the steps of: preparing a carcass structure comprising at least one carcass ply having end flaps in engagement with respective annular anchoring structures disposed concentric with a geometric rotation axis of the tire at axially spaced apart positions with respect to each other; applying a belt structure to the carcass structure at a radially outer position thereof; applying a tread band to the belt structure at a radially outer position thereof; applying a pair of sidewalls to the carcass structure at opposite side positions; incorporating at least one pair of resilient stiffening inserts into the carcass structure concurrently with preparation of said at least one carcass ply.
Tires for vehicle wheels essentially comprise a carcass structure consisting of one or more carcass plies that, in the most classic embodiments, have the respective inner circumferential edges turned up around inextensible annular inserts being part of annular reinforcing structures, disposed at radially opposite positions at the tire regions usually identified as xe2x80x9ctire beadsxe2x80x9d.
A belt structure is applied to the carcass ply or plies at a radially outer position thereof, which belt structure comprises one or more belt layers radially superposed upon each other. A tread band of elastomer material radially overlaps the belt structure. The outer sides of the carcass structure are also covered with respective sidewalls also made of elastomer material.
It should be also pointed out, for the purposes of the present description, that by the term xe2x80x9celastomer materialxe2x80x9d it is meant the rubber blend in its entirety, i.e. the assembly formed of at least one base polymer suitably amalgamated with reinforcing charges and/or process additives of different types.
In order to give the tire self-supporting qualities, i.e. the capability of ensuring short/medium runs in the absence of inflating pressure when a puncture occurs for example, the expedient of integrating into the tire, close to the sidewalls thereof, one or more reinforcing inserts of elastomer material is known, which inserts of semicircular outline and usually identified as xe2x80x9clunettesxe2x80x9d conveniently support the vehicle load when the normal inflating pressure of the tire fails.
In this connection, different embodiments have been proposed aiming at giving the required self-supporting features to the tire, without impairing ride comfort too much when the tire is inflated. These solutions are essentially diversified both in the physico-chemical features of the elastomer materials employed in making the resilient stiffening inserts, and in the contemplated insert number, and also in their positioning in relation to the carcass ply or plies.
Good results, particularly in connection with the tire self-supporting capability under deflated conditions have been achieved with embodiments in which at least one of the resilient stiffening inserts which are present at each sidewall is enclosed between two carcass plies forming a sort of closed container around it, as described in documents GB 2087805, EP 475258 and EP 542252, for example.
The Applicant has however sensed that placing the resilient stiffening inserts in a sort of closed container defined by the carcass plies turned up around the annular anchoring structures tends to increase the tire sidewall rigidity too much not only with reference to its vertical flexibility, i.e. in connection with stresses substantially radial to the rotation axis of the tire, but also with reference to its torsional sensitivity, i.e. in connection with stresses directed tangentially of the circumferential extension of the tire itself.
By adopting particular expedients, as described for example in documents EP 475258 and EP 542252 in the name of the same Applicant, the possibility of restricting, within some limits, the vertical rigidity of the tire sidewall with an inflated tire under running conditions has been achieved. On the other hand, these technical solutions tend to make the tire structure more complicated and heavy and do not appear to be efficient for the purpose of controlling torsional rigidity which has been identified by the Applicant as one of the decisive factors for ride comfort above all at medium/high speeds. In fact, the tire capability of absorbing impacts transmitted by potholes or other unevennesses present on the roadway depends on the torsional rigidity of the tire itself.
The Applicant has also sensed that when the tire runs under normal inflated conditions and, all the more reason, under deflated conditions, the presence of resilient stiffening inserts completely enclosed between two carcass plies imposes strong stresses and/or deformations to the inserts themselves and also to the other constructional components of the tire that are present close to the sidewalls, which will bring about an increase in the operation temperatures and softening of the materials. Due to the above, use of materials having high moduli of elasticity is imposed, which will further reduce ride comfort with an inflated tire.
In accordance with the present invention it has been found that as regards manufacture of self-supporting tires, unexpected advantages can be achieved if the tire carcass structure is formed with a plurality of strip-like lengths sequentially disposed along the circumferential extension of the tire. In this way it is in fact possible to regulate, depending on requirements, the control degree exerted by the carcass structure on the resilient stiffening inserts present therein.
In more detail, it is an object of the present invention to provide a self-supporting tire for vehicle wheels, characterized in that said at least one carcass ply comprises: axially inner strip-like lengths and axially outer strip-like lengths, said axially inner and axially outer lengths being circumferentially distributed around said rotation axis and extending each in a U-shaped configuration around the cross-section outline of the carcass structure, to define two side portions spaced apart from each other in an axial direction and a crown portion extending at a radially outer position between the side portions, said resilient stiffening inserts being each axially interposed between side portions of the axially inner lengths and side portions of the axially outer lengths.
The presence of axially intermediate strip-like lengths may be also provided and they are circumferentially distributed around said rotation axis and extend each in a U-shaped configuration around the cross-section outline of the carcass structure, to define two side portions that, at an axially outer position, overlap said resilient stiffening inserts, and a crown portion extending at a radially outer position between the side portions; and a pair of auxiliary resilient stiffening inserts each axially interposed between the side portions of the axially intermediate lengths and the side portions of the axially outer lengths.
In more detail, the axially inner lengths can be distributed following a circumferential pitch corresponding to a multiple of their width, the axially intermediate lengths are distributed following a circumferential pitch corresponding to a multiple of their width and have each the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially inner lengths, to define a first carcass ply together with the latter, and the axially outer lengths are distributed following a circumferential pitch substantially corresponding to their width, to define a second carcass ply which is radially superposed on the first carcass ply close to said crown portions.
The presence of second axially intermediate strip-like lengths may be also provided which are circumferentially distributed around said rotation axis and extend each in a U-shaped configuration around the cross-section outline of the carcass structure, to define two side portions partly overlapping, at an axially outer position, the side portions of the first axially intermediate lengths, and a crown portion extending at a radially outer position between the respective side portions.
In particular, the axially inner lengths can be distributed following a circumferential pitch substantially corresponding to a multiple of their width, whereas the first axially intermediate lengths are distributed following a circumferential pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially inner lengths, to define a first carcass ply together with the latter, the second axially intermediate lengths are distributed following a circumferential pitch substantially corresponding to a multiple of their width, and the axially outer lengths are distributed following a circumferential pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially intermediate lengths, to define a second carcass ply together with the latter, which second carcass ply is radially superposed on the first carcass ply close to said crown portions.
In a possible alternative embodiment, the axially inner lengths are distributed following a circumferential pitch substantially corresponding to their width, to define a first carcass ply, the axially intermediate lengths are distributed following a circumferential pitch corresponding to a multiple of their width, and the axially outer lengths are distributed following a circumferential pitch corresponding to a multiple of their width and have each the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially intermediate lengths, to define a second carcass ply together with the latter, said second carcass ply being radially superposed on the first carcass ply close to said crown portions.
In a further alternative embodiment the axially inner lengths are distributed following a circumferential pitch substantially corresponding to a multiple of their width, the axially outer lengths having each the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially inner lengths.
Alternatively, the axially inner and axially outer lengths may be provided to be distributed following a circumferential pitch corresponding to the width of each length, to define a first carcass ply and a second carcass ply radially superposed on the first carcass ply close to said crown portions, respectively.
A pair of auxiliary resilient stiffening inserts may be also provided and they are disposed each at an axially inner position with respect to the axially inner lengths.
In a further possible alternative embodiment, each of said strip-like lengths substantially extends in a plane offset in parallel relative to a meridian plane of the tire, so that the respective crown portion, with respect to a radial reference plane passing through the transition point between the crown portion and at least one of the corresponding side portions, is oriented at an angle of different value from the inclination angle of the side portions.
In more detail, the axially inner and axially outer lengths preferably lie in disposition planes that are offset on respectively opposite sides relative to said meridian plane, so that at least the side portions of the axially inner lengths have a crossed orientation with respect to the side portions of the axially outer lengths.
In accordance with a further aspect of the invention, each of said annular anchoring structures has at least one first portion axially interposed between the end portions of the axially inner and axially outer lengths.
In particular, the first portion of each of said annular anchoring structures is preferably provided to comprise: at least one first circumferentially-inextensible annular anchoring insert axially interposed between the end portions belonging to the axially inner and axially outer lengths, respectively; at least one first elastomer filling body extending from said first annular anchoring insert away from the geometric rotation axis and joining the respective resilient stiffening insert.
Each of the annular anchoring structures may in addition comprise at least one second portion disposed at an axially outer position with respect to the end portions belonging to the axially intermediate and the axially outer lengths, respectively.
The second portion too of each of the annular anchoring structures preferably comprises at least one second circumferentially-inextensible annular anchoring insert disposed at an axially outer position with respect to the end portions belonging to the axially outer lengths, and at least one second elastomer filling body extending from said second annular anchoring insert away from the geometric rotation axis.
It may be also provided that each of said annular anchoring structures should further comprise at least one auxiliary portion located at an axially inner position with respect to end portions of the axially inner lengths.
This auxiliary portion preferably comprises at least one auxiliary circumferentially-inextensible annular anchoring insert, disposed against the end portions of the axially inner lengths.
At least one of the above annular anchoring inserts may advantageously comprise at least one thread-like element disposed in radially superposed coils.
It is a further object of the present invention to provide a method of manufacturing a self-supporting tire for vehicle wheels, characterized in that preparation of the carcass structure involves the following steps: preparing strip-like lengths each comprising longitudinal and parallel thread-like elements; laying down axially inner strip-like lengths circumferentially distributed on the toroidal support, each of said axially inner lengths extending in a U-shaped configuration around the cross-section outline of the toroidal support, to define two side portions mutually spaced apart in an axial direction, and a crown portion extending at a radially outer position between the side portions; applying said resilient stiffening inserts at an axially outer position relative to the side portions of the axially inner lengths; laying down axially outer strip-like lengths circumferentially distributed on the toroidal support, each of said axially outer lengths extending in a U-shaped configuration around the cross-section outline of the toroidal support, to define two side portions mutually spaced apart in an axial direction, each extending at an axially outer position relative to one of the resilient stiffening inserts, and a crown portion extending at a radially outer position between the side portions.
In a possible embodiment, before deposition of the axially outer lengths the following further steps are carried out: laying down axially intermediate strip-like lengths circumferentially distributed around said rotation axis and each extending in a U-shaped configuration around the cross-section outline of the carcass structure to define two side portions overlapping, at an axially outer position, said resilient stiffening inserts, and a crown portion extending at a radially outer position between the side portions; applying a pair of auxiliary resilient stiffening inserts at an axially outer position relative to the side portions of the axially intermediate lengths, before deposition of the axially outer lengths.
In particular, it may be provided that the axially inner lengths should be laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, that the axially intermediate lengths should be laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially inner lengths, to define a first carcass ply together with the latter, and that the axially outer lengths should be laid down following a circumferential distribution pitch substantially corresponding to their width, to define a second carcass ply radially superposed on the first carcass ply.
In a possible preferential embodiment, before application of said auxiliary resilient stiffening insert, also carried out is the step of laying down second axially-intermediate strip-like lengths circumferentially distributed around said rotation axis and each extending in a U-shaped configuration around the cross-section outline of the toroidal support, to define two side portions partly overlapping, at an axially outer position, the side portions of the first axially intermediate lengths laid down beforehand, and a crown portion extending at a radially outer position between the respective side portions.
In particular, the axially inner lengths are preferably laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, the first axially intermediate lengths are laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two axially inner lengths, to define a first carcass ply together with the latter, the second axially intermediate lengths are laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, and the axially outer lengths are laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two of said second axially intermediate lengths, to define a second carcass ply together with the latter.
Alternatively, the axially inner lengths can be laid down following a circumferential distribution pitch substantially corresponding to their width, to define a first carcass ply, whereas the axially intermediate lengths are laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, and the axially outer lengths are laid down following a circumferential distribution pitch substantially corresponding to a multiple of their width, each having the respective crown portion interposed in circumferential side by side relationship between the crown portions of two of said intermediate lengths, to define a second carcass ply together with the latter, said second carcass ply being radially superposed on the first carcass ply close to said crown portions.
In a further possible embodiment, the axially inner lengths are distributed following a circumferential pitch substantially corresponding to a multiple of their width, the axially outer lengths being each laid down so that their crown portion is in circumferential side by side relationship between the crown portions of two axially inner lengths.
Alternatively, the axially inner lengths are distributed following a circumferential pitch substantially corresponding to their width, to define a first carcass ply and the axially outer lengths are distributed following a circumferential pitch substantially corresponding to their width, to define a second carcass ply radially superposed on the first carcass ply close to said crown portions.
Also preferably provided is a step of arranging a pair of auxiliary resilient stiffening inserts, disposed each at an axially inner position with respect to the axially inner lengths.
Each of said strip-like lengths may be also laid down in a plane offset in parallel to a meridian plane of the toroidal support.
In particular, the axially inner lengths and axially outer lengths are preferably laid down following deposition planes respectively, that are offset on respectively opposite sides relative to said meridian plane, so that the side portions of the axially inner lengths and axially outer lengths have respectively inclined orientations.
In accordance with a further inventive aspect, accomplishment of each of said annular anchoring structures comprises the step of forming at least one first portion of the annular anchoring structure at an axially outer position relative to the end portions of the axially inner lengths previously laid down on the toroidal support, before deposition of the axially outer lengths.
In particular, formation of the first portion of each of said annular anchoring structures preferably comprises the steps of: applying at least one first circumferentially-inextensible annular insert at an axially outer position relative to the end portions of the axially inner lengths laid down on the toroidal support, applying at least one first elastomer filling body extending from said annular anchoring insert away from the geometric rotation axis and joining the respective resilient stiffening insert.
It may be also provided that accomplishment of said annular anchoring structures should comprise the further step of forming at least one second portion of the annular anchoring structure against the end portions of the axially outer lengths.
Formation of the second portion of each of said annular anchoring structures may advantageously comprise the steps of: applying at least one second circumferentially-inextensible annular anchoring insert at an axially outer position relative to the end portions of the axially outer lengths, applying at least one second elastomer filling body extending from said second annular anchoring insert away from the geometric rotation axis.
Accomplishment of each of said annular anchoring structures may also comprise the step of forming at least one auxiliary portion on the toroidal support before deposition of the axially inner lengths.
Preferably, at least one of said annular anchoring inserts is formed through winding of at least one continuous thread-like element in radially superposed coils.
It is also preferably provided that at least one of said elastomer filling bodies should be formed through winding of at least one continuous thread-like element of elastomer material in coils disposed in axial side by side relationship and/or in radial superposition relationship around the geometric axis of the toroidal support.
Each of said resilient stiffening inserts too can be advantageously formed through winding of at least one continuous thread-like element of elastomer material in coils disposed in axial side by side relationship and/or in radial superposition relationship around the geometric axis of the toroidal support.